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[ilukacevic@fizika.unios.hr]

Hi again

First, I apologize for sending my reply only to M.M. (if I had at all) 
instead of to the list. 
Second, I wish to thank You both D.R. and M.M. for Your help, since the 
calculation now runs nice.

You were right, there are more than 2 atoms per trigonal unit cell in the 
cinnabar phase of ZnTe (I was wrong because I was led by the analogy with a 
NaCl (cubic) phase of the similar II-VI semicond., which, now I realize, has 
a much higher symmetry and thus less atoms per unit cell). In fact, there are 
6 atoms in the unit cell. But, as you both already said, one can use the 
symmetry properties and input only the red. coord. of 2 atoms. These would be 
the 3(a) and 3(b) Wyckoff positions read from the International 
Crystallographic Tables (ICT), under space group P3121, No. 152. 
The .in which works fine is

ecut     40
toldfe   1.0d-8
diemac   12.0

ixc      1
kptopt   3
nshiftk  1
shiftk   0.0  0.0  0.5
ngkpt    8 8 8

#   ZnTe  cinn structure (semiconducting phase)
#   hexagonal (trigonal) unit cell (angdeg, xred)
#   acell: Nelmes&McMahon 1995
acell    7.7573257  7.7573257  17.757756
angdeg   90 90 120
occopt   1
ntime    30
nstep    40
nband    28
spgroup  152
brvltt  -1
natom    6
natrd    2
ntypat   2
typat    1 2
xred
0.540 0.000 1/3
0.504 0.000 5/6
znucl    30.      52.

The complete references are:
1) R.J.Nelmes, M.I.McMahon, N.G.Wright, D.R.Allan, J.Phys.Chem.Solids 56 
(1995), pg 546
2) A.Mujica, A.Rubio, A.Munoz, R.J.Needs, Rev.Mod.Phys. 75 (2003), Table V pg 
902 and pg 906

Now for the M.M.'s comment catch: My line of thinking was that if the ICT 
give us (in the case of the cinnabar phase of ZnTe) the red. coord. of atoms 
in the trigonal coord. system and, as You said, #152 group allows only the 
"spgaxor=1" (which belongs to the hexagonal system), then I would first have 
to transform these red. coord. from the trigonal to the hexagonal coord. 
system using the transformation matrix (which could be found for example in 
G.Burns, A.M.Glazer "Space Groups for Solid State Scientists", pg 50). But, 
as one can see from the .in file, the original red. coord. (given in ICT) 
work fine, as while the transformed ones do not. This still I don't know why.

Again, thank You both.

Igor Lukacevic